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Analysis of Onion Management Practices as they relate to levels of Aspergillus niger (Black Mold) and Development of IPM scouting protocols for Black mold 2000

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Principal Investigators: Teresa Rusinek, CCE Ulster County; John Mishanec, Area IPM Vegetable Educator, Eastern NY

Cooperators: Prof. James Lorbeer, Cornell University, Orange County Onion Growers, Maire Ullrich, CCE Orange County

Abstract:

Black mold (Asperigillus niger) has increasingly been a problem for Orange county onion growers. In 1999 we intended to see if the procedure of rolling early season onions with green tops, prior to harvest, was creating wounds and openings through which wind blown and/or soil borne inoculum of black mold was infecting the outer scales of onion bulbs. Black mold favors high temperatures. Temperatures generally are quite warm during late July and early August when rolling usually occurs. We also looked at undercutting, lifting and windrowing. We thought these practices might reduce black mold by drying the onions without making wounds.

The summer of 1999 was very dry. For most of the Orange county onion-growing region, rainfall was well below average or practically non-existent. The entire onion crop went down early. This situation did not allow for growers to roll their onions. We were able to compare undercutting, lifting and windrowing and found surprising results. Results showed increased black mold incidence when onions were undercut, lifted or windrowed.

In 2000, we repeated the investigation to see if we would get similar results. Prof. James Lorbeer tested Aspergillus niger levels in the soil from the fields involved in the investigation. Soil samples taken this year correlate the highest inoculum levels with fields that have had the least rotation out of onions. The field with the highest soil inoculum rating was also the only field that showed onions with a detectable % of BM before and after storage. The 2000 season was cool and wet; overall incidence of black mold in onion bulbs was low probably due to weather conditions. Because of this it is difficult to draw conclusions based on the data collected this year. Data collected over the past three years on % black mold by variety can help researchers narrow down control options and perhaps guide growers to less susceptible varieties. In the past two years, four scouts have been trained to identify Aspergillus niger in the field. Historically, we have not been able to detect black mold in the field until bulbs are very close to maturity. It therefore stands to reason that scouting for black mold just prior to harvest is most practical. This information will help growers make better harvest and storage management decisions.